The effects of hormones on the induction of ornithine decarboxylase (ODC) in vivo and in liver epithelial cells in culture are being studied. Previous studies have shown that ODC induction may be a marker for tumor promoters. Hormones often increase the activities of complete carcinogens. ODC is used to study the degree of biochemical similarity between hormones and promoters. The present studies indicate that growth hormone and prolactin each induce high levels of ODC in the liver and kidneys of both male and female rats, while cortisone induces hepatic ODC only. Estradiol inhibits, while testosterone increases, the ODC induction by growth hormone. Hormonal effects on tissue levels of S-adenosylmethionine decarboxylase and polyamines will also be determined.